"I think it's an easy go-to, especially a mom on the run," one parent said. "When I want a snack, it's convenient."

Earlier this year, the FDA told KIND bars to stop using the word healthy, because that term is reserved for foods relatively low in fat. But no KIND bars have less than 4 grams of fat, and some have 16 grams.

"So the issue with bars is that really, they're full of sugar, fat and salt," registered dietitian and nutritionist Maya Feller said.

Feller analyzed two popular bars -- the Larabar and a Kit-Kat -- that contain more than 200 calories.

The Kit-Kat has a gram less protein and a little more fat, but the Larabar has more sugar.

The Larabar does have more fiber, but "at the end of the day," Feller said. "They're quite similar."

A macadamia nut with white chocolate Clif bar was comparable to Reese's Peanut Butter Cups and an egg white. Even adding the egg white to match the protein, Feller says the Cliff bar still has more calories and more fat, while both have 21 grams of sugar.

ABC News reached out to the manufacturers, and the makers of the Lara bar said their bar has only real food ingredients: dates, semi-sweet chocolate chips, almonds, walnuts, cocoa powder and sea salt. And they asked, "Which of these ingredients would your nutritionist not recommend as individual food?"

The makers of the Clif bars said, "Clif bar is an energy bar specifically crafted for athletes and active people to deliver balanced nutrition and a convenient source of sustained energy."

And that convenience is a factor. But Feller suggests air-popped popcorn, nuts, boiled eggs and fruit can be just as easily packed.

"Go for a fresh, unprocessed, whole food," she said.

But it's a task easier said than done for those who consistently eat on the go.